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Accumulation of cerebrospinal fluid in a foal’s brain.


  • Enlarged skull

General Information:

  • Fluid exerts pressure on brain and skull.
  • Affected foals are stillborn.
  • Can lead to complications during birth → endangers mare.

Inheritance: autosomal recessive

→ Only animals with two copies of the variant (hcp/hcp) are affected. Animals with only one copy of the variant (N/hcp) are clinically normal carriers.

Possible Genotypes:

Genotype The horse is:
N/N normal. The horse has no copies of the genetic variant causitive for hydrocephalus and therefore cannot pass it on to its offspring.
N/hcp a carrier. The horse is clinically healthy.  It has one copy of the genetic variant causitive for hydrocephalus, which will be passed on to its offspring with a probability of 50%.
hcp/hcp affected. The horse is affected and will not live long enough to reproduce.



  • Carriers may be bred to normal animals (N/hcp x N/N) without any risk of producing affected offspring. The offspring should also be tested before breeding to determine if they are carriers or normal.
  • Breeding two carriers (N/hcp x N/hcp) is not recommended due to the possibility of 25% of the offspring being affected.

Test information: This test detects the change of a single basepair in exon 12 of the B3GALNT2 gene.

Ducro, B.J., Schurink, A., Bastiaansen, J.W., Boegheim, I.J., van Steenbeek, F.G., Vos-Loohuis, M., Nijman, I.J., Monroe, G.R., Hellinga, I., Dibbits, B.W., Back, W., Leegwater, P.A.: A nonsense mutation in B3GALNT2 is concordant with hydrocephalus in Friesian horses. BMC Genomics 16:761, 2015. Pubmed reference: 26452345. DOI: 10.1186/s12864-015-1936-z.

Further information is available at Online Mendelian Inheritance in Animals.

Breeds affected:

Test #: H117

Samples: Blood, Hair

Price: 35 € (net)

Time required: 10-14 days

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